Overhead cranes for transporting heavy items from one location to another within a designated area are well-known in the art. Such cranes basically comprise: (a) a bridge spanning the distance between a pair of rails; (b) motorized end trucks mounted on each end of the bridge that engage the rails to move the bridge along the rails; (c) a motorized trolley mounted for movement along the bridge; (d) a motorized hoist mounted on the trolley for raising and lowering an object to be moved; (e) a pendant or radio control device that allows an operator to generate operator control signals; and (f) a crane control panel that controls the motors in the end trucks, the trolley, and the hoist according to the operator control signals. The operator can control these various motors to move the objected suspended by the hoist within a designated area defined between the rails.
In a number of situations, it is possible for the objects suspended by the hoist to collide with other objects. For example, more than one crane are often mounted on a given set of rails. Should these cranes be operating near each other with objects suspended therefrom, it is very possible that the objects suspended by the two cranes could contact each other. In other cases, at least one end of the rails may abut a wall. An object suspended from a crane operating near the wall may collide with the wall.
It would thus be highly desirable if cranes could be controlled in a manner that reduces the likelihood that the cranes or objects suspended therefrom will come into contact with other objects.